St Andrew’s Cross Spider
- Colour: the female has a silvery head with silver, yellow, red and black bands across its abdomen, and two yellow stripes running down its underside. Its legs are dark brown to black with one or two yellowish bands. The male and juveniles are brown and cream, with brown legs.
- It often appears to have only four legs because it sits with its legs in pairs, forming a cross pattern.
- Distinctive feature: the zigzag patterns (known as the stabilimentum) it weaves into its web to form an X – after which it is named.
- Size: the female is 1 – 2 cm long but the tiny male is only 3 – 5 mm long (body length).
- Diet: insects, including flies, moths, butterflies, grasshoppers and bees caught in its web, which is strung between low shrubs and long grass. The prey is wrapped in silk and eaten straight away or hung nearby for later, although smaller prey may be bitten first.
- Movement: the female usually hangs upside down on the underside of the web, in the centre, with its legs resting in pairs and placed along each arm of the webbed cross. It occupies the web continuously and is active at various intervals throughout the day and night. If threatened, it will either drop from the web or shake the web so vigorously that it and the webbed cross become a blur, confusing any potential attacker. The male usually builds a smaller web close to the female, or sits on the outskirts of the female’s web, on the top side.
- Breeding: from summer to autumn. Several males will often sit on the upper outskirts of a web, on the opposite side to the female, waiting for an opportunity to mate with her. The male constructs a mating thread within the web which he vibrates to attract the female. After mating, the female wraps several pear-shaped, green egg sacs in a network of silk and suspends them in nearby vegetation or from a wall.
What to Observe
- How Many Females Present
- Number of Males on Web
- Number of Egg Sacs in Web
ClimateWatch Science Advisor
Spiders may start appearing earlier in the year as a result of climate change warming the earth, and they may also start breeding earlier and appearing in areas that were previously too cold for them. However, at present in some areas, spiders have been appearing much later in the year than expected due to fluctuating temperatures and rain.
When To Look
- Day or night throughout summer (when they are most prevalent) and also in autumn.
Where To Look
- In eastern Australia, including Queensland, New South Wales and Victoria.
- In a variety of habitats including rainforest edges, open forest, woodlands, grasslands and urban areas. It is particularly common in suburban gardens.
- Look between low shrubs and long grass, and also against the walls of buildings. Its web is commonly 1 – 2 metres above the ground (generally around waist height) and about one metre in diameter. Look in your backyard garden during summer.
The map below displays the accumulated observations of these species as reported by ClimateWatch observers, together with the layer showing how the range of the species might change between now and 2085, with orange areas indicating where the species might disappear, and green areas where the species range might expand.
Eisner T and Nowicki S 1983. Spider web protection through visual advertisement: role of the stabilimentum. Science 219: 185-187.
McKeown, K 1963. Australian Spiders. Angus and Robertson, Sydney.
York Main, B 1976. Spiders. The Australian Naturalist Library, Collins.
- Painted Orb Weaver (Argiope picta): less common than the St Andrew’s Cross Spider and doesn’t normally produce a complete X pattern on its web.
- Banded orb-weaving spider (Argiope trifasciata): has yellow, white and black bands on its abdomen, and dark brown and pale yellow bands along the entire length of its legs.
Did You Know?
There are many theories about why the female weaves the cross into its web, including strengthening the web, for camouflage, and for enhancing prey catches as the cross reflects ultra-violet light which attracts insects. It may also deter predators which must go to the effort of cleaning off the extra silk after diving into the web.
Its predators include birds and humans (who destroy the webs), with wasps and flies known to target egg sacs.
Many males are attacked and eaten by the female during courtship!